Matched coupling apparatus



June 2 1964 R. LA ROSA 3,135,924

MATCHED COUPLING APPARATUS Filed June 27, 1960 2 Sheets-Sheet 1 TERMINATION IBIL FIG. 1a

r- 1 l S :1 l8 A I3 39 :r-u": I20. a l9 June 2, 1964 R. LA ROSA 3,135,924

MATCHED COUPLING APPARATUS Filed June 27, 1960 2 Sheets-Sheet 2 TERMINATION Q, I i %34 4| 4 2 g V//////////// FT/////////// 4 FIG. 2a

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FIG. 2b

FIG. 3

United States Patent Ofi 3,135,924 Patented June 2, 1964 ice General This invention relates to apparatus for coupling a wave guide to a shielded transmission line termination. While the termination will be described as a coaxial device, it is obvious that the invention is not limited thereto.

This application is a continuation-in-part of application Serial No. 844,356, filed October '5, 1959, now abandoned.

In the past, those skilled in the art have experienced considerable difficulty in constructing matched coupling apparatus for coupling a wave guide to a shielded transmission line termination such as a coaxial device where the termination, connected directly or through an intervening, coaxial line, presents a higher impedance at coaxial terminals in a wall of the wave guide than the internal impedance of the Wave guide. The means devised have been inefiicient, and complicated. In a specific case where the coaxial device is a crystal detector, it has been It is an object of the present invention to provide new and improved matched coupling apparatus between a Wave guide and a shielded transmission line termination.

It is another object of the present invention to provide matched coupling apparatus between a wave guide and a shielded transmission line termination which is simple in construction and efficient in operation.

It is a further object of the present invention to provide matched coupling apparatus between a Wave guide and a shielded transmission line termination where the impedance at the shielded transmission line terminals, due to the termination, is higher than the internal impedance of the wave guide.

It is still a further object of the present invention to provide matched coupling apparatus between a wave guide and'a coaxial device which is simple in construction and efficient in operation.

It is yet a further'object of the present invention to provide matched coupling apparatus between a wave guide and a crystal detector which is simple in construction, efiicient in operation and which provides a convenient output for a detected signal.

In accordance with a particular form of thepresent invention, matched coupling apparatus comprises a Wave guide having coaxial transmission line terminals in a first wall thereof, a termination connected to these terminals presenting an impedance at the terminals which is higher than the internal impedance of the Wave guide and a post of cross-section larger than the inner conductor of the terminals connected at one end to the wave guide wall opposite the first wall and at the other end to the inner conductor, the post forming an LC circuit composed primarily of the combination of the capacitance between the end of the post and the first wall and the inherent inductance of the post; the apparatus being so constructed and arranged that the LC circuit formed by the post has an impedance higher than the internal impedance of the wave guide and is effective to match the higher impedance presented at the terminals.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring to the drawings: FIG. 1a shows matched coupling apparatus constructed in accordance with the present invention;

FIG. 1b shows the equivalent circuit of the apparatus of FIG. 1a;

FIG. 2a shows matched coupling apparatus between a Wave guide and a crystal detector; 2 FIGCi 2b shows the equivalent of the apparatus of FIG.

a, an

FIG. 3 shows wave forms useful in the explanation of the operation of the FIGS. 2a and 2b apparatus.

Description of Apparatus of FIG. 1a

FIG. 1a shows matched coupling apparatus constructed 1n accordance with the present invention. The apparatus includes a Wave guide 10 having shielded transmission line terminals 11a, 11b, shown dotted, in a wall 12 of the wave guide. A shielded transmission line is composed of one or more inner conductors, all operating at than the internal impedance of the wave guide 10. The

apparatus additionally includes a post 15 protruding from a wall 16 of the wave guide 10 toward the opposite wall 12 so as to form an LC circuit betweenthe walls.

post 15 is connected to the inner conductor 11a.

Operation 0] Apparatus of FIGS. 1a and 1b The following explanation of the operation of the matched coupling apparatus will describe thewave guide 10 as a source of a signal and the termination 13 as a load to which the signal is to be coupled. It will be apparent that the functions of the wave guide and the;

termination may be reversed inthat the termination 13 may be a source of a signal, such as a generator, and the wave guide 10 may be the load to which the signal is to.

be coupled.

The wave guide 10 supplies a signal which is to be coupled to the termination 13. The termination 13, when connected either directly to the coaxial terminals 11a, 1112 or, as shown, through a length of coaxial line 14, presents an impedance at the terminals 11a, 11b which is higher than the internal impedance of the Wave guide 10. If the length of coaxial line 14 is properly adjusted, the termination 13 may appear as a pure resistance which is large compared to the characteristic impedance of the coaxial line 14.

While the invention is. not limited to any particular shaped Wave guide, a typical expression for the internal impedance. of a rectangular wave guide measured at the center of the broad wall (dimension a below) b is the dimension of the waveguide parallel to the electric field vector where a is the width of the Wave guide measured perpendicular a is one-half The The signal supplied by the wave guide creates a magnetic field which is associated with the currents flowing in the post 15. This magnetic field is represented by the dashed inductance symbol 17 shown on the post 15. The signal supplied by the wave guide 10 also creates an electric field between the top of the post and the wall 12. This electric field is represented by the dashed capacitance symbols 18, 18.

The equivalent circuit of the FIG. 1a apparatus is shown in FIG. 1b. Elements in FIG. 1b corresponding to elements in FIG. la have been given the same reference numerals followed by the suflix a. In FIG. 1b the variable inductor 17a is equivalent to the post 15; the variable capacitor 18a is equivalent to the capacitances 18, 18; and the resistor 13a is equivalent to the termination 13. The signal supplied by the wave guide 10 appears between terminals 12a, 16a representative of the wave guide walls 12 and 15, respectively. The signal coupled to the termination 13 appears across the resistor 13a shown by terminals 19, 19. The parallel resonant circuit 20, shown dashed, is equivalent to the wave guide stub of approximately one-quarter wave length. For all practical purposes, the parallel resonant circuit appears as an open circuit and need not be considered any further.

The termination 13, represented by resistor 13a in FIG. 1b, may be matched to the wave guide 10, represented in FIG. lb by the terminals 12a, 16a, by varying either the inductance of the inductor 17a or the capacitance of the capacitor 18a or both of these parameters. These variations in inductance and capacitance are achieved by varying either the size, shape or position of the post 15. More particularly, the post 15 may take any shape and may, for example, be a cube or a cylinder. The choice of an appropriate shape for the post 15 is one of design. Changing the width of the post 15 primarily changes the inductance of the inductor 17a while also varying the capacitance of the capacitor 18a. On the other hand, moving the post either closer to or farther away from the wall 12, primarily changes the capacitance of the capacitor 18a while also changing the inductance of the inductor 17a. The post may be moved either toward or away from the wall 12 by any simple and convenient mechanical arrangement. Obviously, it is also possible to change the size or shape of the post 15 very simply.

It is apparent that for a given termination 13 and for a given wave guide 10, which has an internal impedance which is much lower than the impedance presented at the terminals 11a, 11b due to the termination 13, the termination may be matched to the wave guide 10 by changing the inductance and capacitance of inductor 17a and capacitor 18a, respectively. This is accomplished by changing the dimensions of the post 15 and its position relative to the wall 12. In this manner, the signals supplied by the wave guide 10 may be coupled to the termination 13 with minimum losses. Since the ratio of inductance to capacitance determines the transformation ratio and the product of inductance and capacitance determines the tuning for proper frequency, it may only be necessary to change either the size or position of the post if the first approximation of size and position results in a near correct transformation ratio or proper frequency.

Description and Operation of Apparatus of FIGS. 2a and 212 FIG. 2a shows matched coupling apparatus between a wave guide and a crystal detector. In this embodiment, the apparatus includes wave guide means 30 having shielded transmission line terminals 31a, 31b, shown dotted, in a wall 32 of the wave guide. Means 30 supply a radio-frequency carrier signal modulated by video infor mation. As shown in FIG. 2a, the shielded transmission line terminals may be coaxial terminals having a single inner conductor 31a surrounded by a shield or outer conductor 31b. The apparatus also includes a termination 33, such as a crystal detector, connected to the terminals 31a, 31b either directly or, as shown, through a length of transmission line 34. The termination 33 again presents an impedance at the terminals 31a, 31b which is higher than the internal impedance of Wave guide means 30. The apparatus also includes a post 35 protruding from a wall 36 of wave guide means 30 toward the opposite wall 32 so as to form an LC circuit between the walls. Included within the post 35 is a conventional resonant trap 37 so designed as to be properly tuned to the frequency of the radio-frequency carrier signal. The apparatus also includes a shaft 38 running through the post 35, one end thereof being connected to an inner conductor of the shielded transmission line terminals and the other end thereof being projected through the wave guide means 39 to furnish the video information. In particular, the shaft 38 is connected at one end to the inner conductor 31a while the other end thereof is projected through the wall 36. Furthermore, the shaft 38 is insulated from the post 35 and the wave guide wall 36 by insulators 39, 40, 41, 42, 43 and 44.

The termination 33 may be matched to wave guide means 3% in the same manner as the termination 13 was matched to the wave guide 10 in FIG. 1. The radiofrequency carrier signal supplied by wave guide means 30 creates a magnetic field associated with currents flowing in the post 35 and an electric field between the top of the post and the wall 32. The magnetic field acts as an inductance while the electric field represented by capacitors 45, 45 acts as a capacitance. The equivalent circuit of the apparatus of FIG. 2a is shown in FIG. 2b. Elements in FIG. 2b corresponding to elements in FIG. 2a have been given the same reference numbers followed by the suflix a. In FIG. 2b the variable inductor 35a is equivalent to the post 35; the variable capacitor 45a is equivalent to the capacitance between the top of the post 35 and the wall 32; and the crystal detector 33a is equivalent to the termination 33. The signal supplied by wave guide means 30 appears between terminals 32a, 36a, representative of the walls 32 and 36, respectively. The signal coupled to the termination 33 appears across the crystal 33a shown by terminals 46, 46. The parallel resonant circuit 47, shown dashed, is similar to the one described in FIG. 1b.

The wave forms of FIG. 3 will be useful in the explanation of the operation of the FIG. 2a apparatus. Wave form A shows the signal supplied by the wave guide means 30 as being composed of a radio-frequency carrier signal modulated by video information. The signal supplied by wave guide means 30 may be coupled to the termination 33, or more particularly, the crystal detector 33a, with minimum losses, by adjusting the value of the inductance of inductor 35a and the capacitance of capacitor 45a in a manner previously described in connection with the FIG. 1a apparatus. The signal coupled to the crystal detector 33a is rectified thereat and due to the polarity of the crystal detector as shown in the drawing, only the negative portions of the radio-frequency carrier signal remain. This is shown in wave form B in FIG. 3. It is obvious that the polarity of the crystal detector 33a need not be as shown but may be reversed. The rectified signal, represented by wave form B, appears along those portions of the shaft 38 which are external to the post 35. Since the resonant trap 37 is tuned to the frequency of the radio-frequency carrier signal, only the video information appears along those portions of the shaft 38 which are within the resonant trap. The resonant trap 37 effectively prevents the radio-frequency carrier signal from entering the post 35. In effect, an impedance exists between the post 35 and the shaft 38 in the resonant trap 37 which is low with respect to the radio-frequency signal and which is high with respect to video. The equivalent circuit shows this radio-frequency impedance as dashed line 43. The desired detected video information, shown in wave form C of FIG. 3, is, therefore, available between the terminals 49, 49 shown in the equivalent circuit, or more particularly, at the lower end of the shaft 38 which is projected through the wall 36. The specific advantage of using the resonant trap 37 in the manner indicated, is that the radio-frequency circuit is broken at a point where the radio-frequency currents are small. In particular, the impedance between the shaft 38 and the post 35 looking out into the radiofrequency circuit, is very high. This high impedance allows the use of a low capacitance resonant trap, thereby allowing greater band width.

While there have been described what are at present considered to be the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. Matched coupling apparatus comprising: wave guide means, having shielded transmission line terminals in a wall thereof, for supplying a radio-frequency carrier signal modulated by video information; a rectifier connected to said terminals presenting an impedance at said terminals which is higher than the internal impedance of said wave guide means; a post protruding from one wall of said wave guide toward the opposite wall so as to form an LC circuit between the walls, said post including therewithin a resonant trap for said carrier; and a shaft run ning through saidpost, one end thereof being connected to an inner conductor of said terminals and the other end thereof being projected through said Wave guide means to furnish said video information; the parameters of the apparatus being such as to match said termination to said wave guide.

2. Matched coupling apparatus comprising: wave guide means having coaxial terminals in a wall thereof, for

supplying a radio-frequency carrier signal modulated by video information; a rectifier connected to said terminals presenting an impedance at said terminals which is higher than the internal impedance of said wave guide means; and a post protruding from one wall of said wave guide toward said first mentioned wall so as to form an LC circuit between the walls, said post including therewithin a resonant trap for said carrier; and a shaft running through said post, one end thereof being connected to an inner conductor of said terminals and the other end thereof being projected through said wave guide means to furnish said video information; the parameters of the apparatus being such as to match said termination to said wave guide.

3. Matched coupling apparatus comprising: a wave guide having coaxial transmission line terminals in a first wallthereof; a termination connected to said terminals presenting an impedance at said terminals which is higher than the internal impedance of said wave guide; and a post of cross-section larger than the inner conductor of said terminals connected to the wave guide wall opposite said first wall, said post forming an LC circuit composed primarily of the combination of the capacitance between the end of the post and said first Wall and the inherent inductance of the post; the apparatus being so constructed and arranged that the LC circuit formed by said post has an impedance higher than the internal impedance of said wave guide and is effective to match said higher impedance presented at said terminals.

References Cited in the file of this patent UNITED STATES PATENTS 2,659,055 Cohn Nov. 10, 1953 2,954,468 Matthaei Sept. 27, 1960 2,956,160 Sharpless Oct. 11, 1960 3,028,560 Saad Apr. 3, 1962 FOREIGN PATENTS 468,538 Canada Oct. 3, 1950 988,968 France Sept. 3, 1951 

1. MATCHED COUPLING APPARATUS COMPRISING: WAVE GUIDE MEANS, HAVING SHIELDED TRANSMISSION LINE TERMINALS IN A WALL THEREOF, FOR SUPPLYING A RADIO-FREQUENCY CARRIER SIGNAL MODULATED BY VIDEO INFORMATION; A RECTIFIER CONNECTED TO SAID TERMINALS PRESENTING AN IMPEDANCE AT SAID TERMINALS WHICH IS HIGHER THAN THE INTERNAL IMPEDANCE OF SAID WAVE GUIDE MEANS; A POST PROTRUDING FROM ONE WALL OF SAID WAVE GUIDE TOWARD THE OPPOSITE WALL SO AS TO FORM AN LC CIRCUIT BETWEEN THE WALLS, SAID POST INCLUDING THEREWITHIN A RESONANT TRAP FOR SAID CARRIER; AND A SHAFT RUNNING THROUGH SAID POST, ONE END THEREOF BEING CONNECTED TO AN INNER CONDUCTOR OF SAID TERMINALS AND THE OTHER END THEREOF BEING PROJECTED THROUGH SAID WAVE GUIDE MEANS TO FURNISH SAID VIDEO INFORMATION; THE PARAMETERS OF THE APPARATUS BEING SUCH AS TO MATCH SAID TERMINATION TO SAID WAVE GUIDE. 